Nowadays foam material is used as stuffing for a boat, which has the advantage of high strength and bearing of high load. Even it is damaged, water cannot leak into an external surface of a ship. Hence it is often applied to lifeboats, transport boats and fishing boats.
At the side of a boat, there is at least a holding hole seat, for setting a flagpole, a fishing rod and so on. A conventional holding hole seat normally comprises an inner ring and an outer ring, wherein the outer ring is extending at the bottom and thereby building up a cylindrical through hull fitting; wherein the inner ring and outer ring are screwed together, whereby an external surface of a ship is pressed between the inner ring and the outer ring. Thereby it is achieved that the cylindrical through hull fitting is set in an external surface of a ship for holding flagpole, fishing rod and so on.
A conventional inner ring and cylindrical through hull fitting are formed mostly in one piece made of PVC. However, heat resistance and strength of the cylindrical through hull fitting made of PVC are limited. During injecting foam material into the ship side layer, the cylindrical through hull fitting can become deformed or broken.
Besides, since fixing of the inner ring in the external surface of a ship is only possible through connection with the outer ring, the inner ring and the cylindrical through hull fitting are pressed in the ship side layer, as soon as the outer ring is taken down, while the external surface of a ship is still not filled with foam material.
In view of these disadvantages the inventor performed continuous testing and improvement and developed the present invention.